摘要：本文介紹了9個GaussDB常用的對象語句，希望對大家有幫助。

本文分享自華為云社區《GaussDB對象相關語句》，作者：酷哥。

1. 常用函數

pg_database_size() -- 數據庫使用的磁盤空間。 pg_table_size() -- 表使用的磁盤空間。 pg_total_relation_size() -- 表和索引共使用的磁盤空間。 pg_indexes_size() -- 索引使用的磁盤空間。

2. 常用系統表

pg_class -- 存儲數據庫對象信息及其之間的關系。 pg_index -- 存儲索引的一部分信息，其他的信息大多數在PG_CLASS中。 pg_namespace -- 存儲schema相關的信息。 pg_database -- 存儲數據庫相關的信息。

3. 常用視圖

pg_stat_user_tables -- 顯示所有用戶自定義普通表和toast表的狀態信息。 pg_stat_user_indexes -- 顯示數據庫中用戶自定義普通表和toast表的索引狀態信息。

4. 常用語句

4.1查詢庫大小

select datname, pg_database_size(datname), pg_database_size(datname)/1024/1024/1024 as "dataSize_GB" FROM pg_database where datname not in ('template1', 'template0');

4.2查看schema的所有者

-- pg_user這個視圖只有sysadmin用戶有權限查，普通用戶無法查詢。 SELECT s.nspname schema_name,u.usename schema_owner FROM pg_namespace s, pg_user u WHERE nspname = '$schema_name' AND s.nspowner = u.usesysid;

4.3獲取表結構

set current_schema to $schema; select pg_get_tabledef('$table_name'); 或 select pg_get_tabledef('$schema_name.$table_name');

示例：

select pg_get_tabledef('testschema.t1'); pg_get_tabledef ---------------------------------------- SET search_path = testschema; + CREATE TABLE t1 ( + id integer, + name character varying(15) + ) + WITH (orientation=row, compression=no)+ DISTRIBUTE BY HASH(id) + TO GROUP group_version1; (1 row)

4.4查詢表大小

-- 查詢單個確定表的大小。 select pg_table_size('$schema_name.$table_name'); -- 不包含索引，單位B select pg_total_relation_size('$schema_name.$table_name'); -- 包含索引，單位B -- 查詢連接的數據中，所有用戶表的大小 SELECT schemaname,relname, pg_total_relation_size(concat(schemaname,'.',relname))/1024/1024/1024 table_size_GB FROM PG_STAT_USER_TABLES ORDER BY 3 DESC; -- 包含索引 SELECT schemaname,relname, pg_table_size(concat(schemaname,'.',relname))/1024/1024/1024 table_size_GB FROM PG_STAT_USER_TABLES ORDER BY 3 DESC; -- 不包含索引" SELECT table_name,pg_size_pretty(table_size) AS table_size,pg_size_pretty(indexes_size) AS indexes_size,pg_size_pretty(total_size) AS total_size FROM (SELECT table_name,pg_table_size(table_name) AS table_size,pg_indexes_size(table_name) AS indexes_size,pg_total_relation_size(table_name) AS total_size FROM (SELECT concat(table_schema,concat('.',table_name)) AS table_name FROM information_schema.tables where table_schema ilike '$schema_name') AS all_tables ORDER BY total_size DESC) AS pretty_sizes;

示例

-- 查詢單個確定表的大小。 select pg_table_size('testschema.t1'); pg_table_size --------------- 17801216 (1 row) -- 查詢連接的數據中，所有用戶表的大小 SELECT schemaname,relname, pg_total_relation_size(concat(schemaname,'.',relname))/1024/1024/1024 table_size_GB FROM PG_STAT_USER_TABLES ORDER BY 3 DESC; -- 包含索引 schemaname | relname | table_size_gb ------------+--------------+-------------------- testschema | t_ran2 | 2.288818359375e-05 testschema | t_ran1 | 1.52587890625e-05 testschema | t_ran3 | 1.52587890625e-05 -- 需要指定schema SELECT table_name,pg_size_pretty(table_size) AS table_size,pg_size_pretty(indexes_size) AS indexes_size,pg_size_pretty(total_size) AS total_size FROM (SELECT table_name,pg_table_size(table_name) AS table_size,pg_indexes_size(table_name) AS indexes_size,pg_total_relation_size(table_name) AS total_size FROM (SELECT concat(table_schema,concat('.',table_name)) AS table_name FROM information_schema.tables where table_schema ilike 'testschema') AS all_tables ORDER BY total_size DESC) AS pretty_sizes; table_name | table_size | indexes_size | total_size -------------------------+------------+--------------+------------ testschema.t_ran2 | 24 kB | 0 bytes | 24 kB testschema.t_ran3 | 16 kB | 0 bytes | 16 kB testschema.t_ran1 | 16 kB | 0 bytes | 16 kB

4.5查看表的統計信息

-- 查看指定schema和table的統計信息。 select * from pg_stat_user_tables where schemaname = '$schema_name' and relname = '$table_name'; -- 查詢全庫的表的活躍元組數、死元組數及死元組占比。 select schemaname, relname, n_live_tup, n_dead_tup, (n_dead_tup/(n_live_tup+1)) as dead_rating from pg_stat_user_tables order by rating desc,n_dead_tup desc limit 30; -- 查看表大小及活躍元組、死元組、死元組比例。 select schemaname, relname, pg_size_pretty(table_size) as table_size, pg_size_pretty(indexes_size) as indexes_size, pg_size_pretty(total_size) as total_size, round((total_size / pg_database_size(current_database())) * 100,2) as "percent(%)", n_live_tup,n_dead_tup,(n_dead_tup/(n_live_tup+1)) as dead_tuple_rating from (select schemaname, relname, pg_table_size(concat(schemaname,'.',relname)) as table_size, pg_indexes_size(concat(schemaname,'.',relname)) as indexes_size, pg_total_relation_size(concat(schemaname,'.',relname)) as total_size,n_live_tup,n_dead_tup from pg_stat_user_tables) order by "percent(%)" desc;

示例：

select schemaname, relname, pg_size_pretty(table_size) as table_size, pg_size_pretty(indexes_size) as indexes_size, pg_size_pretty(total_size) as total_size, round((total_size / pg_database_size(current_database())) * 100,2) as "percent(%)", n_live_tup,n_dead_tup,(n_dead_tup/(n_live_tup+1)) as dead_tuple_rating from (select schemaname, relname, pg_table_size(concat(schemaname,'.',relname)) as table_size, pg_indexes_size(concat(schemaname,'.',relname)) as indexes_size, pg_total_relation_size(concat(schemaname,'.',relname)) as total_size,n_live_tup,n_dead_tup from pg_stat_user_tables) order by "percent(%)" desc; schemaname | relname | table_size | indexes_size | total_size | percent(%) | n_live_tup | n_dead_tup | dead_tuple_rating ------------+--------------+------------+--------------+------------+------------+------------+------------+------------------- testschema | t_ran2 | 24 kB | 0 bytes | 24 kB | .01 | 4 | 0 | 0 testschema | t_ran1 | 16 kB | 0 bytes | 16 kB | .01 | 3 | 0 | 0 testschema | t_ran3 | 16 kB | 0 bytes | 16 kB | .01 | 6 | 0 | 0

4.6查詢數據是否傾斜

SELECT a.count,b.node_name FROM (SELECT count(*) AS count,xc_node_id FROM table_name GROUP BY xc_node_id) a, pgxc_node b WHERE a.xc_node_id=b.node_id ORDER BY a.count desc;

4.7查詢給定分布鍵歸屬的DN

select * from pgxc_node where node_id = (select xc_node_id from $table where $col = $value limit 1);

示例

select * from pgxc_node where node_id = (select xc_node_id from t1 where id = 1); node_name | node_type | node_port | node_host | node_port1 | node_host1 | hostis_primary | nodeis_primary | nodeis_preferred | node_id | sctp_port | control_port | sctp_port1 | control_po rt1 | nodeis_central | nodeis_active -------------------+-----------+-----------+--------------+------------+--------------+----------------+----------------+------- dn_xxx | D | 45700 | 10.30.41.163 | 45700 | 10.30.41.163 | t | f | f | -564789568 | 45702 | 45703 | 0 | 0 | f | t

4.8查詢表的主鍵

select pg_constraint.conname as pk_name from pg_constraint inner join pg_class on pg_constraint.conrelid = pg_class.oid where pg_class.relname = '$table_name' and pg_constraint.contype = 'p';

4.9查詢事務信息

select xmin, xmax, * from $table_name;

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